The present invention relates to a novel organopolysiloxane and, more particularly, relates to an organopolysiloxane which has a branching structure in the neighborhood of one terminal of the molecular chain and which contains the silicon-bonded hydrogen group at each of the resulting derivative terminals. The invention also relates to a method for the preparation of this organopolysiloxane.
It is already well known that organopolysiloxanes containing various types of organofunctional groups may be prepared by a hydrosilylation reaction between SiH group-containing organopolysiloxane and an organic compound whose molecule contains both an aliphatically unsaturated group as well as any of various organofunctional groups. With regard to the organofunctional organopolysiloxanes obtained in this manner, the fundamental structure in terms of number of functional groups and so forth is directly determined by the starting SiH group-containing organopolysiloxane.
Because the organopolysiloxanes used for such modifications are generally prepared by an equilibration polymerization reaction between SiH group-containing organopolysiloxane and SiH group-free organopolysiloxane, the product therefrom takes the form of a mixture of different degrees of polymerization. Thus, the product's chemical structure can be no more than an average, and, accordingly, the number of silicon-bonded hydrogen groups in the individual molecules is also an average. This poses the problem that the number of functional groups in the final organofunctional organopolysiloxane product is also only an average.
However, while the modification of organic polymeric compounds by organofunctional organopolysiloxane has entered into widespread use in the fine chemicals sector, this has occurred at the same time as an increasing requirement for strict control over the number of functional groups. As a particular matter, the use of organofunctional organopolysiloxane in polycondensation reactions requires the systematic introduction of only two functional groups into each molecule. Nevertheless, in the case of organofunctional organopolysiloxane based on SiH group-containing organopolysiloxane obtained by an equilibration polymerization reaction, even when two functional groups are present on average, organopolysiloxane is present which not only contains 2 functional groups, but also, for example, zero, one, or three or more functional groups. This engenders such problems as gelation during the process, or activity as a reaction terminator, or residual unreacted material in the system.
In order to avoid these problems, it has been proposed that the SiH group-containing organopolysiloxane be prepared by a non-equilibration polymerization reaction. Thus, organopolysiloxane containing the terminal silicon-bonded hydrogen group can be prepared by the ring-opening polymerization of hexamethylcyclotrisiloxane using alkyllithium or lithium silanolate as the polymerization initiator, followed by termination of the reaction using dimethylchlorosilane and so forth. However, only 1 silicon-bonded hydrogen group can be introduced at the corresponding molecular terminal in this method, which accordingly creates the restriction that only a single organofunctional group can be introduced at the molecular chain terminal.
In contrast to this, in order to obtain graft copolymers between organofunctional organopolysiloxane and other organic polymers, it would be desirable to have two organofunctional groups clustered or segregated at one terminal. Nevertheless, neither the corresponding starting organopolysiloxane having two silicon-bonded hydrogen groups clustered at one terminal nor a method for the preparation of such an organopolysiloxane have been available up to the present time.